Harbour porpoises and plastics

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Harbour porpoises and plastics

Gepubliceerd op
8 januari 2018

About 15% of harbour porpoises found dead on beaches in the Netherlands has ingested plastic in the stomach. This is shown in a recent publication by Wageningen Marine Research and the Faculty of Veterinary Medicine (Utrecht University).

Dietstudy and plastic

Wageningen Marine Research has a long track record in study of the diet of beached harbour porpoises. Non-food items in the stomachs were recorded, but not following a strict method suitable dedicated to plastic monitoring. Following this early approach, about 7% of the animals were noted to have plastic in the stomach

Standard method

In more recently analysed samples of stomachs the diet analyses were supplemented with the standard method used in the EU for monitoring plastic abundance in the stomachs of northern fulmars and marine turtles. This addition implies that all stomach contents are filtered over a 1mm sieve and studied under the microscope. Using this standard approach, plastics were recorded in 15% of the animals.

Beached dead harbour porpoise found on Texel, The Netherlands, 8-Jan-2009
Beached dead harbour porpoise found on Texel, The Netherlands, 8-Jan-2009

Surrounding areas

Studies from other countries bordering the North Sea report far less plastics, at most 1 to 2%. But usually those studies only visually inspected stomachs during autopsies. In order to obtain a proper view of regional differences or trends over time, the standard method with the 1mm sieve will be necessary.

Benthic debris

The findings suggest that harbour porpoises mainly accidentally ingest plastics when foraging on fish close to the bottom. In many cases, harbour porpoises that contained plastics, had also ingested other natural bottom debris, such as shell fragments and bog-wood (semifossil wood derived from old surfaced peat layers in the bottom of the North Sea). Stomach contents of northern fulmars mainly reflect plastics pollution near the water surface, but harbour porpoises, like seals could thus act as an relative indicator for plastic abundance near the bottom of the sea.

Citation and downloads

A single pdf file combining the article and the large online supplement is available for download here:

The stomach of harbour porpoise #UT0145 contained a large plastic washer
The stomach of harbour porpoise #UT0145 contained a large plastic washer
Harbour porpoise #UT0153 had a piece of silicon rubber plus large pieces of bog-wood in its stomach
Harbour porpoise #UT0153 had a piece of silicon rubber plus large pieces of bog-wood in its stomach
Harbour porpoise #UT0238 had a fishhook with piece of nylon line in the stomach. As a loose item, such a fishhook may be relatively harmless, and degrades quicker than the nylon line. Only when there is tension on the fishline, substantial damage may be caused, but such was not the case in this animal. (photo Bert Aggenbach, NIOZ)
Harbour porpoise #UT0238 had a fishhook with piece of nylon line in the stomach. As a loose item, such a fishhook may be relatively harmless, and degrades quicker than the nylon line. Only when there is tension on the fishline, substantial damage may be caused, but such was not the case in this animal. (photo Bert Aggenbach, NIOZ)
Extreme stomach content of harbour porpoise #TX0012, with sheetlike plastic litter, but also small pebbles, a shell, crab remains, a bird feather and bog-wood
Extreme stomach content of harbour porpoise #TX0012, with sheetlike plastic litter, but also small pebbles, a shell, crab remains, a bird feather and bog-wood